Moisture resistant biomass fuel compact and method of manufacturing

ABSTRACT

A method of processing a biomass fuel compact is provided that includes combining a composition of combustible biomass materials, comminuting the composition of biomass materials, adding an adhesive to the biomass materials to form a composite biomass, the adhesive having a starch and a hydroxide, forming the composite biomass into a shapeform, and heat treating the composite biomass shapeform at a base temperature sufficient to break O—H bonds, the base temperature being below a mean torrefication temperature of the composite biomass such that torrefaction of a substantial portion of the biomass materials does not occur.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.13/018,155, titled “Biomass Fuel Compact Processing Method” filed onJan. 31, 2011, the contents of which are incorporated herein byreference in their entirety.

FIELD

The present disclosure relates to renewable energy sources, and inparticular, resources that do not depend on fossil fuels and that reduceemissions of “greenhouse gas” carbon dioxide into the atmosphere. Morespecifically, the present disclosure relates to manufacturing processesfor creating combustible biomass, or biofuel materials.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

With the recent emphasis on renewable energy sources, efforts have beenmade in the art to create so-called “biomass” materials, in which acombustible combination of waste, such as wood chips or sawdust, alongwith certain additives, are combined and processed to create an energyresource that can take the place of, or be combined with, for example,coal. A common biomass is the wood pellet, which is now subject to astandard developed by the Pellet Fuels Institute. More specifically, a“premium” oak species wood pellet provides 8810 BTU/lb, and a “standard”pine species wood pellet provides 9600 BTU/lb. Furthermore, both ash andchlorine content are provided by the standard.

Known biomass materials contain natural lignins, which are released withheat of the constituent materials in order to bind the materialstogether into a burnable mass. Natural lignins, for example from variouswood sources, are complex natural polymers resulting from oxidativecoupling of, primarily, 4-hydroxyphenylpropanoids. Additionally, othermaterials such as thermoplastic resins have been used to bind theconstituent materials together.

However, these natural lignins and thermoplastic binders do not create abiomass that is durable for transport or other processing operations.Moreover, these biomass forms suffer from chronic crumbling and dustgeneration during production and downstream handling. Significantamounts of dust can become an explosive issue, and thus current bindersin the art may ultimately cause safety hazards. As a furtherdisadvantage of known binders, product uniformity is an issue, withirregular lengths and ragged cuts, which further add to the dustproblem. As other materials without natural lignins are added, such asswitchgrass, forest litter, paper waste, cane waste, corn stover, grasshay, and the like, product quality is reduced, and the dust issue oftenbecomes more aggravated. Additionally, some of the known bindersgenerate gases during the burning process that are environmentallyundesirable, and in fact, some of the binders are not completelycombusted during the burning process.

An additional handling issue with biomass fuel sources is moistureabsorption. Due to their porous nature, biomass materials are prone tomoisture absorption and subsequent degradation during transportation andstorage. Additionally, bacteria can develop in biomass materials thatcontain moisture, which leads to the production of methane and thus asignificant risk factor in transportation and storage. Efforts have beenmade to use additional binders and/or to further process the biomassfuel sources in order to provide moisture resistance. However, theseefforts are often costly and require significant additional processingenergy, thereby reducing the cost and environmental benefits of biomassas an alternative fuel source.

SUMMARY

In one form of the present disclosure, a method of processing a biomassfuel compact is provided that comprises combining a composition ofcombustible biomass materials, comminuting the composition of biomassmaterials, adding an adhesive to the biomass materials to form acomposite biomass, the adhesive consisting of a starch and a hydroxide,forming the composite biomass into a shapeform, and heat treating thecomposite biomass shapeform at a base temperature sufficient to breakO—H bonds, the base temperature being below a torrefication temperatureof the composite biomass such that torrefaction of the biomass materialsdoes not occur. Various biomass fuel compacts manufactured according tothe methods of the present disclosure are also provided.

In another form, a method of processing a biomass fuel compact isprovided that comprises heat treating biomass materials of the biomassfuel compact at a base temperature sufficient to break O—H bonds, thebase temperature being below a torrefication temperature of the biomassfuel compact such that torrefaction of the biomass materials does notoccur.

In still another form, a method of processing a biomass fuel compact isprovided that comprises heat treating biomass materials of the biomassfuel compact at a base temperature sufficient to break O—H bonds, thebase temperature being below a mean torrefication temperature of thebiomass fuel compact such that torrefaction of a substantial portion ofthe biomass materials does not occur.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

In order that the disclosure may be well understood, there will now bedescribed various forms thereof, given by way of example, referencebeing made to the accompanying drawings, in which:

FIG. 1 is a process flow diagram illustrating the various steps andforms of the manufacturing processes according to the teachings of thepresent disclosure;

FIG. 2 is a process flow diagram illustrating the various steps andforms of another manufacturing processes according to the teachings ofthe present disclosure;

FIG. 3 a is a photograph of a sample biomass fuel compact manufacturedaccording to the teachings of the present disclosure;

FIG. 3 b is a photograph of a container filled with sample biomass fuelcompact shapeforms defining sectors, and more specifically quadrants,manufactured according to the teachings of the present disclosure;

FIG. 4 is a perspective view of a biomass fuel compact manufacturedaccording to the teachings of the present disclosure and having ashapeform defining a cylindrical sector in accordance with one form ofthe present disclosure; and

FIG. 5 is a photograph of an experimental test conducted on the quadrantshapeforms after passing through a conventional coal chute, illustratinga relatively even distribution without any binding, bridging, or lodgingwithin the delivery chute.

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses.

Referring to FIG. 1, manufacturing steps for processing a biomass fuelcompact, and variations thereof, are shown. It should be understood thatthese steps may be carried out in order as shown, or alternately, in adifferent order. Therefore, the order of the steps illustrated shouldnot be construed as limiting the scope of the present disclosure. In oneform, the method of processing a biomass fuel compact comprisescombining a composition of biomass materials. These biomass materialsare essentially any combustible material, or combination of combustiblematerials. For example, these materials may include saw dust, cardboardand chipboard, grass, switchgrass, energy crops, hay, tree bark,sweetgum seed pods, pinecones, newsprint, wheat straw, duckweed, pineneedles, mixed leaves, yard waste, agricultural waste, cotton waste,grape and wine offal, corn stover, crop stovers, peat, tobacco waste,tea waste, coffee waste, food processing waste, food packaging waste,nut meats and shells, chestnut hulls, pecan shells, animal waste,livestock waste, mammal waste, municipal solid waste, paper waste,pallets, and egg cartons, among others. Other combustible materials mayalso be employed, and thus these biomass materials should not beconstrued as limiting the scope of the present disclosure.

Next, these biomass materials may be comminuted, or crushed, to aparticle size that is compatible with the specific process, and alsowith other additives and various processing steps, as set forth ingreater detail below. The comminuted composition of biomass materialsmay next be dried, or alternately, the comminuted composition of biomassmaterials may be wet before entering a forming step, again depending ona variety of processing parameters. For example, if a tree or woodproducts were used as part of the biomass composition, then thecomminuting step would take these materials down to a sawdust form. Thecomminution process may be carried out, for example, by tub grinders,horizontal grinders, hammer mills, burr mills, or shredders, amongothers. Each type of biomass material will have a different derivedparticle size from the comminuting step. Generally, particle sizerequirements are based on desired throughput rates. In one form of thepresent disclosure, a particle size that is about 20 to about 40%, andmore particularly about 30%, of the die opening/diameter used to producethe desired shapeform. These particle sizes facilitate flow rateswithout excessive processing back-pressure.

If the biomass materials are dried before entering the forming step, amoisture content of about 8% to about 20%, and more specifically about12%, is typical for many types of biomass materials. In one form of thepresent disclosure, the drying is performed by low cost solar collectortroughs that concentrate solar energy and heat suitable thermal mediumssuch as oil, antifreeze, water, or a mixture thereof, for transmissionof heat energy through liquid to air heat exchangers. Alternately,geothermal drying may be employed, alone or in combination withgas-fired or electric drying processes. Drying equipment may also beconventional grain drying batch hoppers, bins, or silos, or higherthroughput horizontal dryers. Further still, heat may be transferredthrough a passive floor heating system. In yet another form, single ormultiple desiccant beds may be employed to remove moisture from thedrying air. It should be understood that these drying methods are merelyexemplary and thus should not be construed as limiting the scope of thepresent disclosure.

An advantageous step of the present disclosure involves adding anadhesive to the biomass materials, wherein the adhesive comprises astarch and a hydroxide.

Advantageously, the biomass fuel compact is highly durable do to itsinventive adhesive additive. Generally, the biomass fuel compact uses aStein Hall type adhesive made from starch, or any other suitablematerial to replace the natural lignins as set forth above. In a SteinHall adhesive, about 5% to 20% of the total starch content isgelatinized into a high viscosity paste called primary starch. Theremainder of the starch (about 80% to 90%) stays ungelatinized and iscalled secondary starch. The starch may be one produced from wheat,oats, rice, corn, wheat middling, wheat waste or even wood and the like,but containing a gelatinized fraction that upon substantial drying willtightly bond the biomass composition.

Additionally, the adhesive additive includes a hydroxide. The hydroxidemay be, for example, alkali metal hydroxides, alkaline earth hydroxides,sodium hydroxide, potassium hydroxide, calcium hydroxide, lithiumhydroxide, and caustic soda, among others. The synergistic combinationof starch and hydroxide provide a highly durable biomass fuel compact,in which any number of constituent combustible materials may be used,without relying on any natural lignins or other undesirable binders.

In one form, the innovative adhesive is provided to bind the constituentbiomass composition and also to form a substantially continuous shellaround the exterior portion of the fuel compact. With this shell, thebiomass fuel compact according to the present disclosure is highlydurable and significantly reduces the traditional dust issues associatedwith biomass compositions, as set forth above.

In one exemplary composition of the present disclosure, the biomass fuelcompact comprises, by percent weight, about 69-98% biomass composition,about 1-30% starch, and less than 1% hydroxide. Another composition isabout 90-95% biomass and about 5-10% of the inventive adhesive additive.

Further additives are also provided by the present disclosure, which mayinclude, by way of example, a silicate additive, (which may be a liquidor powder form), a viscosity additive, a preservative, and a BTUadditive. The silicate additive is included to provide added weatherresistance and hydrogen bonding of biomass particles. The silicate mayinclude sodium, potassium, or lithium, or mixtures of these three in oneform of the present disclosure. The viscosity additive may be anaturally occurring biomass such as duckweed reduced to a flour particlesize, or rice hulls, or coal dust, or any other viscosity alteringsubstance. The preservatives may include, by way of example, fungicides,biocides, or mixtures of these two, in one form of the presentdisclosure. In another form, the preservative may include sodiumtetraborate or borax containing compounds at a concentration of about 1to about 5%, and more particularly, about 1 to about 2%. Moreover,sodium silicate may be added to improve water repellency and act as abiocide, along with any oil, natural or petroleum based, used motor oil,or oil derivatives as the BTU additive.

The additives may also include materials that will benefit thecombustion or emission profile of the biomass. When calcium hydroxide isused as a source of hydroxide, it may react to form calcium silicate,which scavenges sulfur dioxide and nitrous oxides in air emissions fromcombustion in flue gas. When lithium hydroxide is used, it may react andform lithium silicate, which forms a zeolite capable of sequesteringcarbon dioxide from combustion gases. Furthermore, it is contemplatedthat the addition of a mix of alkali metal or alkaline earth hydroxidesmay be beneficial to the emission of undesirable gases from combustionof the innovative compacts according to the teachings of the presentdisclosure.

Each of the viscosity additive and the BTU additive, in one form of thepresent disclosure, are combustible materials. The viscosity additive,in one form, is a naturally occurring biomass such as duckweed, ricehulls, and coal dust. Furthermore, by way of example, the BTU additiveis an oil or an oil derivative, either natural or petroleum based, andeither new, off specification, or waste oil.

In a further exemplary composition, the biomass fuel compact comprisesabout 50-95% biomass, about 5-50% starch, about 0.005-0.05% hydroxide,about 0.1-5% silicate additive, and about 0.1-2% viscosity additive orpreservative. In should be noted that the BTU additive may compriseabout 1 to about 40% of the final fuel compact composition. Furthercompositions according to the teachings of the present disclosure areset forth below in Table 1, with an exemplary target value for onebiomass composition that comprises grass, corn stover, or a mixturethereof, according to the teachings of the present disclosure:

TABLE 1 Biomass Starch Hydroxide Silicate Viscosity Preservative BTURange 50-90% 1-50% 0.005-0.05% 0-5% 0-15% 0-2% 0-30% Target 60 4 0.022.5 2 0.48 25

According to the various compositions of the present disclosure, anenergy content of about 8,500 BTU/lb is achieved with the claimedbiomass fuel compact.

After or during the introduction of additives, the composite biomass isformed into a shapeform. In one form of the present disclosure, theforming step is performed by an extrusion process. Other manufacturingprocesses may also be employed, including but not limited to compressionmolding, plunger molding, and die forming. Therefore, the extrusionprocess should not be construed as limiting the scope of the presentdisclosure. In one desired form of the present disclosure, the extruderpremixes, extrudes, and cuts to length a composite biomass fuel compactat about 500 to about 30,000 pounds per hour.

In one form, the innovative adhesive is added at a throat portion of theextruder. Alternately, the adhesive is added in a hopper portion of theextruder. In still another form, the adhesive is added in a die portionof the extruder and is configured to coat an exterior surface area ofthe composition of biomass materials. The adhesive may be furtherdivided within the processing step, wherein the starch is mixed with thebiomass composition prior to forming, and the hydroxide is added duringthe forming. Alternately, the hydroxilazed, gelled starch is addedbetween the throat and before the forming die. Additionally, steam maybe used as a processing aid during forming in order to provide forbetter physical properties of the biomass composition and additives.

With plunger molding, in one form the adhesive is added between wads ofthe plunger. Alternately, the adhesive is added at a plunger input andis configured to coat an exterior surface area of the composition ofbiomass materials at an exit die.

It is further contemplated that a mechanical briquetting process, suchas the Brik Series by Dipiu Macchine Impianti, Italy, or BHS Energy LLC,Wyoming, Pa., USA, may be employed in accordance with the teachings ofthe present disclosure.

The shapeform of the composite biomass may be any number of geometricconfigurations, including but not limited to pellets, briquettes, pucks,and the innovative corn kernel configuration as described in thecopending application set forth above.

After the composite biomass is produced as a shapeform, it ispartitioned into individual pieces. The individual pieces may be thesame size, or of varying sizes/lengths. In one form, the individualpieces are compatible with any existing powerplants. These existingpowerplants comprise, by way of example, combustion, power generation,gasification, ethanol, digestion, and steam generation plants.

In one form of the present disclosure, the processing is performed atlower temperatures such that an endothermic reaction of the biomassmaterials and adhesive results. These temperatures are in the range ofabout 200 to about 250° F. for an extrusion process, and similarly,about 25 to about 200° F. for other plunger or flywheel processes.

Moisture Resistance

Referring now to FIG. 2, another form of the present disclosure involvesadditional manufacturing steps in order to provide improved moistureresistance in the biomass fuel compact. More specifically, the methodinvolves heat treating biomass materials of the biomass fuel compact ata base temperature sufficient to break O—H bonds, the base temperaturebeing below a torrefication temperature of the biomass fuel compact suchthat torrefaction of the biomass materials does not occur. And in oneform, the biomass materials are heat treated at a base temperature beingbelow a mean torrefication temperature of the biomass fuel compact suchthat torrefaction of a substantial portion of the biomass materials doesnot occur.

By way of background, thermal and chemical treatment of biomasstypically fall in the following temperature ranges:

Dehydration: about 382° F. (194° C.) to about 455° F. (235° C.);

Rectification: about 455° F. (235° C.) to about 482° F. (250° C.); and

Torrification: about 482° F. (250° C.) to 518° F. (270° C.). (It shouldbe noted, however, that some sources indicate broadly that torrefactionoccurs between 200° C. and 300° C.).

Further, biomass is generally comprised of hemicelluloses, cellulose,and lignin with each type varying in content for a particular biomasstype as well as its response to thermal treatment.

According to the present invention, it has been determined that wateradsorption characteristics are positively affected by heat treatment ofthe biomass in order to break O—H bonds. The response to low temperaturetreatment in the range of about 120° F. to about 455° F. using ovensand/or microwave energy-induced heating, or infrared (IR) inducedheating, produced a weather/moisture resistant biomass fuel compact.Referring to FIG. 3 a, an example of such a biomass fuel compact thathas been heat treated is illustrated and generally indicated byreference numeral 100. Various biomass materials were processed over atemperature range of 120° F. to 590° F. in an inert atmosphere in orderto determine that the target temperature need not be as high astorrefication or even rectification for most biomass materials in orderto provide a sufficient amount of moisture resistance. According to thepresent disclosure, a “base temperature” for the biomass materials is alower temperature (about 120° F. to about 455° F. as set forth above)that produces a Maillard-like reaction, a non-enzymatic reaction thatproduces browning of some food stuffs, such as bread and coffee beans.Therefore, as used herein, a base temperature shall be construed to meana temperature sufficient to break O—H bonds, the base temperature beingbelow a mean torrefication temperature of the biomass fuel compact suchthat torrefaction of a substantial portion of the biomass materials doesnot occur.

In one form of the present disclosure, coarse ground biomass is heattreated up to about 455° F. to dehydrate in conventional dryers. In oneform, this is accomplished in two steps. First, in a rotary kiln, suchas a triple-pass dryer for effluent drying down to about 5-10% moisturecontent. A second step can be in a conventional oven, microwave or thelike with an inert atmosphere such as carbon dioxide, followed by afinal size and particle reduction to suit the follow-on compactionequipment. A higher temperature heat treatment of about 250° F.-450° F.in a carbon dioxide atmosphere enhances cell disruption to releaseintersticial moisture, thereby rendering the biomass friable. It shouldbe understood that at temperatures in the lower portion of the range ofthe present disclosure (near about 120° F.), it is possible tosufficiently heat treat the biomass materials in an environment that isnot inert. Therefore, an inert heat treating environment should not beconstrued as limiting the scope of the present disclosure.

One form of the present disclosure uses a high wattage microwave, forexample from about 90 to about 3,200 watts, to perform the heattreatment. However, certain biomass materials are transparent tomicrowave energy. These include most grasses, and grain stover.Therefore, by the addition of a few percent of microwave receptors, suchas woody biomass, nut shells, coffee grounds or the like, the biomasscomposition can be properly heat treated according to the teachings ofthe present disclosure. In one form, the microwave heat treatment iscontinuous with the other processing steps of combining, comminuting,adding the adhesive, and forming the composite biomass, among otherpossible processing steps. As a continuous process, the biomassmaterials are passed through a sealed microwave environment without aninterruption of opening and closing the microwave environment.

Referring now to FIGS. 3 b and 4, a novel shapeform 120 is provided bythe present disclosure. As shown, the shapeform 120 is a sector, and inone form is ¼ of a cylindrical puck (shown in FIG. 3 a) to define aquadrant. This quadrant form is relatively simple to manufacture bycutting the cylindrical puck of FIG. 3 a into equal quarters. It shouldbe understood, however, that this shapeform and variations/derivativethereof may be manufactured by other processes such as molding orgrinding, by way of example, and thus partitioning the cylindrical puckas set forth above should not be construed as limiting the scope of thepresent disclosure.

Referring to FIG. 5, the quadrant shapeform was tested in a conventionalcoal chute to determine how well it would distribute in a holding areaor combustion floor and if it was susceptible to binding, bridging, orlodging within the delivery chute on its way to a destination. In thistest, the quadrant shapeform was dropped through a coal chute, throughfuel distribution ports, and to the floor of a solid fuel boiler. Abatch of conventional coal (shown as black pieces on floor of holdingarea) was first distributed within the holding area in order to compareits distribution with the novel quadrant shapeform (shown as the lighterpieces on floor of holding area) of the present disclosure. As shown,the quadrant shapeform exhibited an excellent and relatively evendistribution within the holding area that was comparable to the coaldistribution. Therefore, the quadrant shapeform demonstrated suitabilityto be used within existing coal processing equipment, thereby providingfurther benefits from the biomass compact according to the teachings ofthe present disclosure.

In another form of the present disclosure, an oil coating is applied toat least a portion of the composite biomass shapeform after heattreating. This oil coating may be sprayed onto, or the biomass may bedipped into a bath of oil, by way of example. The oil coating isprovided in order to further improve the moisture resistance of thebiomass fuel compact, and to increase its BTUs when fired. The oil maybe used restaurant waste, used motor oil, or hydraulic fluids, by way ofexample.

It should be noted that the disclosure is not limited to the embodimentdescribed and illustrated as examples. A large variety of modificationshave been described and more are part of the knowledge of the personskilled in the art. These and further modifications as well as anyreplacement by technical equivalents may be added to the description andfigures, without leaving the scope of the protection of the disclosureand of the present patent. For example, the combining and comminutingsteps as shown in FIG. 2 may be performed in either order, and the heattreating may occur on the raw biomass materials prior to adding theadhesive as shown. Further, the adhesive need not be the starch andhydroxide as set forth herein, or an adhesive may be omitted alltogether while remaining within the scope of the present disclosure.

1. A method of processing a biomass fuel compact comprising: combining acomposition of combustible biomass materials; comminuting thecomposition of biomass materials; adding an adhesive to the biomassmaterials to form a composite biomass, the adhesive comprising a starchand a hydroxide; forming the composite biomass into a shapeform; andheat treating the composite biomass shapeform at a base temperaturesufficient to break O—H bonds, the base temperature being below atorrefication temperature of the composite biomass such thattorrefaction of the biomass materials does not occur.
 2. The methodaccording to claim 1 further comprising applying an oil coating to atleast a portion of the composite biomass shapeform after heat treating.3. The method according to claim 1, wherein the heat treating isperformed in an inert environment.
 4. The method according to claim 1,wherein the heat treating is performed in a microwave apparatus.
 5. Themethod according to claim 4, wherein the composite biomass shapeform isheat treated by the microwave apparatus in a continuous process.
 6. Abiomass fuel compact manufactured according to the method of claim 4,wherein the combustible biomass materials include at least a portion ofmicrowave receptors.
 7. The method according to claim 1, wherein theheat treating is performed in a temperature range of about 120° F. toabout 455° F.
 8. A biomass fuel compact manufactured according to themethod of claim
 1. 9. The biomass fuel compact according to claim 8,wherein the shapeform defines a cylindrical sector.
 10. The biomass fuelcompact according to claim 9, wherein the cylindrical sector is aquadrant.
 11. A method of processing a biomass fuel compact comprisingheat treating biomass materials of the biomass fuel compact at a basetemperature sufficient to break O—H bonds, the base temperature beingbelow a torrefication temperature of the biomass fuel compact such thattorrefaction of the biomass materials does not occur.
 12. The methodaccording to claim 11, wherein the heat treating is performed after thebiomass fuel compact is formed into a shapeform.
 13. The methodaccording to claim 11, wherein the heat treating is performed on thebiomass materials before the biomass fuel compact is formed into ashapeform.
 14. The method according to claim 11 further comprisingadding an adhesive to the biomass materials to form a composite biomass,the adhesive comprising a starch and a hydroxide, wherein the compositebiomass is further processed into a shapeform.
 15. The method accordingto claim 11 further comprising applying an oil coating to at least aportion of the biomass fuel compact after heat treating.
 16. The methodaccording to claim 11, wherein the heat treating is performed in aninert environment.
 17. The method according to claim 11, wherein theheat treating is performed in a microwave apparatus.
 18. The methodaccording to claim 17, wherein the biomass fuel compact is heat treatedby the microwave apparatus in a continuous process.
 19. A biomass fuelcompact manufactured according to the method of claim 17, wherein thebiomass materials include at least a portion of microwave receptors. 20.The method according to claim 11, wherein the heat treating is performedin a temperature range of about 120° F. to about 455° F.
 21. A biomassfuel compact manufactured according to the method of claim
 11. 22. Thebiomass fuel compact according to claim 21 having a shapeform defining acylindrical sector.
 23. The biomass fuel compact according to claim 22,wherein the cylindrical sector is a quadrant.
 24. A method of processinga biomass fuel compact comprising heat treating biomass materials of thebiomass fuel compact at a base temperature sufficient to break O—Hbonds, the base temperature being below a mean torrefication temperatureof the biomass fuel compact such that torrefaction of a substantialportion of the biomass materials does not occur.